Filtering diaphragms



Waited States Patent Inventor Guy .I. J. Marie Neuilly-sur-Selne, France Appl. No. 728,803 Filed May 13, 1968 Patented Nov. 17, 1970 Assignee Societe DEtudes Pour Parois Filtrantes Parfil Paris, Victor-Hugo, France a company Priority May 16, 1967 France No. PV106,487

FILTERING DIAPHRAGMS 3 Claims, No Drawing U.S. Cl 210/483, 210/508 Int. Cl 801d 39/18, 801d 31/00 Field of Search 210/22, 23, 321 500, 506, 508, 483

[56] References Cited UNITED STATES PATENTS 3,405,058 10/1968 Miller 210/321X FOREIGN PATENTS 224,114 3/1958 Australia 210/508 OTHER REFERENCES Loeb et al., Sea Water Demineralization by Means of an Osmotic Membrane" from Advances in Chemistry Series, received in Patent Office Nov. 12, 1963, pp.1 17-129 relied Primary Examiner Reuben Friedman Assistant Examiner-F rank A. Spear, Jr. Attorney-Jacobs & Jacobs ABSTRACT: A filtering diaphragm intended for osmotic exchanges and molecular separations constituted by a sheet of microporous paper made of regenerated cellulose fibres which have been subjected to a marked fibrillation, said sheet being coated with a tenuous sheet of plastic material such as silicone elastomer having osmotic properties. If said coat is reduced to submicronic thickness, the diaphragm can serve for molecular separations e.g. the removal of salt out ofsea water.

FILTERING DIAPHRAGMS exchanges through diaphragms which are generally made of 1 an elastomer; the thinner said diaphragm the better are the yields of the osmotic exchanges.

However, the production of such diaphragms is a very delicate matter, since their reduced thickness involves brittleness.

It is also a known fact that such diaphragms may be obtained by tangentially cutting cylindrical parts made of a suitable material, but such technique is difficult and therefore expensive of execution and does not allow obtaining sheaths of a thickness under 2 microns.

It has also been proposed to embed within the mass of a suitable plastic material a textile fabric made of very thinthreads forming large meshes. This leads to the formation of a reinforced osmotic diaphragm constituted by a multiplicity of menisci the thickness of which decreases towards the'center of each mesh.

Consequently, the thickness of the diaphragm cannot be constant throughout and only the central section of each mesh has a sufficiently reduced thickness.

My invention has for its object a comparatively cheap osmotic diaphragm the thickness of which is both constant and extremely reduced.

My improved osmotic diaphragm is a microporous sheet of paper, that is a sheet of paper with very fine pores, carrying a coating film as tenuous as possible, made of a plastic material having osmotic properties.

Preferably, the microporous paper is constituted by a paper the pores of which have an average diameter smaller than onefiftieth micron.

Preferably, said paper is made of regenerated cellulosic fibres which have been refined so as to show a considerable fibrillation, which allows obtaining a felt the micropores of which have diameters ranging between one-fiftieth and onehundredth micron, as is the case of the fibres perfected by the Comptoir du Textile Artificiel and sold under the style Paper BX".

This manner of producing an osmotic diaphragm allows obtaining a diaphragm of a very reduced thickness of a magnitude of l micron, while it provides in spite of this very reduced thickness a perfectly continuous surface, the diaphragm being perfectly strong and its cost price being very low, since the technique of coating by means of a coating machine of the roller type is a very speedy one and its operation is an easy matter.

Furthermore, the diaphragm surface being provided with pores of a very reduced diameter, there is substantially no convergent meniscus formed in registry with each pore and the thickness of the coating of plastic material is thus perfectly constant throughout said diaphragm surface.

EXAMPLE A paper of the BX type produced by starting with regenerated cellulosic fibres which have been refined so as to show a very marked fibrillation, the specific weight of which paper is 30 grs. per sq. m., while its pores have an average diameter ranging between one-fiftieth and one-hundredth micron, is coated by a coating machine of the well-known roller type with a silicone elastomer allowing selective changes between oxygen and carbonic gas.

It has been found that for a like contacting area, the yield of the exchanges was clearly improved when using such a treated paper, chiefly with relation to carbonic acid gas, the actual osmotic coating having a thickness of 1 micron.

It is in fact possible to lay with a coating machine a continuous coat over the sheetof paper with a view to producing an osmotic diaphragm and according to a modification of my invention, i may reduce the thickness of the coating to form a porous submicronic film through which I may obtain a molecular separation through simple filtration. in particular, such a submicronic filter may serve for removing the salt from sea water.

I claim:

1. A filtering diaphragm comprising a paper sheet of regenerated cellulose fibers having a marked fibrillation and having pores of an average diameter less than one-fiftieth micron and a tenuous coating of an osmotic plastic material extending over one of the surfaces of said paper sheet.

2. A diaphragm according to claim 1 wherein the average pore diameter is from one-fiftieth to one-hundredth micron.

3. A diaphragm according to claim 1 wherein the plastic material is a silicone elastomer. 

